The main goal of these investigations is to understand the regulation of lipogenesis exerted at the reaction catalyzed by acetyl CoA carboxylase (ACC) in normal mammary gland and then to evaluate whether ACC's control is lost during mammary tumorigenesis. To meet these objectives, the following types of investigations are being carried out: a) Acetyl CoA carboxylase from lactating rat mammary gland has been purified to approximately 15 i.u. mg minus 1 protein. The physical-chemical characteristics and subunit structure of ACC have been investigated. b) The levels of ACC and fatty acid synthetase (FAS) were measured in the developing mammary gland (virgin, pregnant, lactating) and compared with the results obtained on rat mammary tumors (13762 and R3230 AC) that were grown in animals of similar physiologic state. c) Biotin binding antibodies were raised in rabbits by injecting biotin covalently linked to bovine serum albumin. These antibodies reacted with the protomeric form of mammary gland ACC but not with the polymeric form of the enzyme. The biotin binding antibodies are of potential use in exploring the ligand induced conformational changes that may occur in mammalian ACC.